Near-miss: Suspected high levels of CO₂ in diver breathing gas

A member has reported an incident where there was an elevated level of CO2 in the divers' reclaim breathing gas during saturation diving operations. A dive team was performing diving operations with two divers working on the seabed at an approximate depth of 92 m. The bellman was within the diving bell supporting the two divers in the water.

While working on the seabed the divers began to experience breathing difficulties but this was not reported to the Dive Supervisor. On return to the bell for his hydration break, one of the divers experienced difficulties climbing his umbilical to return to the bell but put this down to his own level of fitness. He mentioned this to the bellman during the hydration break but this was not reported to the Dive Supervisor. On his return to the worksite the diver again experienced breathing difficulties and asked the Dive Supervisor if everything was OK with the reclaim system. On checking the topside reclaim system and discussing his concerns with the bellman, he reported back to the diver that all was OK.

A short while later an alarm sounded on the CO2 analyser for the divers' reclaim return. The Dive Supervisor noted the analyser was displaying an incorrect reading. The divers then subsequently advised the Dive Supervisor of the problems they were experiencing, including; agitation, breathing difficulties and headaches.

The Dive Supervisor requested the divers flush their helmets, go on open circuit, return to the bell stage and changed the divers onto a secondary breathing mix. The Dive Supervisor also raised concerns regarding the analyser and requested that the analyser was changed. The Soda Sorb was also replaced in the divers' reclaim system. Following the change of analyser, it was noted that the CO2 reading displayed was out with normal operating parameters.

Both divers were subsequently recovered to the bell and the dive was aborted with no further ill effects experienced by either of the divers.

A formal investigation was initiated and a report was submitted to the regulatory authorities.

Soda Sorb is used within the diver reclaim system and absorbs CO2 exhaled by the divers. This reclaimed gas is then recirculated through the topside process system and subsequently resupplied back to the divers.

In this incident, the Soda Sorb within the reclaim towers which absorbs the CO2 was allowed to saturate. This resulted in elevated levels of CO2 entering the reclaim loop and the divers experiencing symptoms indicative of an elevated level of CO2 within their breathing gas.

Our Member suggested that the following things went wrong:

• It appears a mistake had been made in calibrating the analysers which resulted in them not alarming at the expected threshold levels.
  
  
• The vessel specific dive system operating procedures did not contain sufficient detail on how to calibrate and set the alarms for the CO2 analysers.
  
  
• Industry practice is that Soda Sorb is changed based on the monitoring of the CO2 alarms.
  
  
• The symptoms experienced by the divers at the time were not considered initially by the diver or supervisor significant enough to cause alarm.
  
  
• The incorrectly calibrated CO2 analyser indicated a fault code. This was not known as a fault code and its significance was not recognised.

Our Member made the following observations:

• It is essential to ensure manufacturers’ equipment guidance is up to date and available to all relevant personnel on board.
  
  
  • Key information provided by the manufacturer must also be reflected in the operating processes and procedures to ensure the safe maintenance and operation of plant and equipment.
    
    
• It is essential to ensure persons responsible for the set up and calibration of equipment are familiar with the procedures for safety critical equipment.
  
  
• It is essential that persons in safety critical roles understand the importance of systems that have single point failures and the value of establishing effective risk control and mitigating barriers.
  
  
• The importance of effective training, competency and on-going assessment for personnel performing a safety critical role.
  
  
  • This should include practical competence assessment, especially if the person performing the safety critical role has been absent from the worksite for an extended period of time.
    
    
• The importance of ensuring that sufficient detail is captured within dive system operating procedures, on how to calibrate and set up analysers including setting of alarms.
  
  
• The importance of ensuring that manuals used across multiple assets are consistent to ensure the same practices are applied.